Utilization of an anhydride as a demulsifier and a solvent for demulsifier formulations

ABSTRACT

The present invention includes the use of anhydride compositions, including alkyl and aryl anhydrides, for use as a demulsifier in resolving emulsions of water and oil. In particular, the anhydride composition can be used alone or in a blend with other demulsifiers. Suitable anhydrides suitable for the present invention include acetic and propionic, with acetic anhydride being preferred. The anhydride composition can be added directly to crude oil or other compositions to be resolved. As such, the demulsifier composition includes an anhydride, such as acetic anhydride, alone or in combination with other demulsifiers. The anhydride can be used in an amount ranging between trace and 100% by weight of the demulsifier composition.

TECHNICAL FIELD

This invention relates to demulsifier compositions and methods forresolving water-in-oil emulsions. More particularly, this inventionrelates to anhydride compositions, such as acetic anhydride, for use asa demulsifier or as a component in demulsifier compositions for use inresolving water-in-oil emulsions. This invention has particularapplicability in cold climates where low temperature stability isrequired.

BACKGROUND

Crude oil produced from geological formations can contain variousamounts of water. Water and crude oil are naturally non-miscible;however, when naturally occurring interfacial active compounds arepresent, these compounds can aggregate on the oil and water interfaceand cause water to form droplets within the bulk oil phase. During crudeoil lifting through production tubings, the oil and water encounters anincreased mixing energy from rapid flow through chokes and bends. Thisadditional mixing energy can emulsify the oil and water. Such an oilexternal, water internal two-phase system is commonly referred to as acrude oil emulsion, which can be quite stable. The presence of water incrude oil, however, can interfere with refining operations, inducecorrosion, increase heat capacity, and result in reduced handlingcapacity of pipelines and refining equipment. Therefore, the crude oilthat is to be shipped out of the oilfield should be practically free ofwater and usually has a maximum water content limit of about 0.5 to 3%by total weight, depending on the type of crude and oil company.

The emulsified water can also contain various amounts of salts. Thesesalts are detrimental to crude oil refining processes due to potentialcorrosion in the refinery. In crude oil refining, desalting techniquescomprise the deliberate mixing of the incoming crude oil with a fresh“wash water” to extract the water soluble salts and hydrophilic solidsfrom the crude oil. Primary dehydration of the crude oil occurs in oilfield water oil separation systems such as “free water knock out” and“Phase separators.” Quite often, these systems are not adequate forefficient separation due to factors such as over production, unexpectedproduction changes, and system underdesigns. In these cases,emulsion-breaking chemicals are added to the production processes toassist and promote rapid water oil separations.

Commonly used emulsion-breaking chemicals or demulsifiers includealkylphenol formaldehyde resin alkoxylates (AFRA), polyalkylene glycols(PAG), organic sulfonates, and the like. These compounds, however, maynot provide satisfactory performance in all instances. In particular, inextremely cold weather (e.g., −40° C. and below) various problems areknown. These active ingredients are typically viscous and require asuitable solvent to reduce the viscosity of the demulsifier blend.Accordingly, there is an ongoing need for new, economical and effectivechemicals and processes for resolving emulsions into the component partsof oil and water or brine, including processes and compositions that aresuitable for cold climates.

Finally, organic acids are commonly used in demulsifier formulations toenhance performance. Organic acids (and occasionally inorganic acids)are sometimes used as separate or supplementary treatments toconventional demulsifier formulations. Such acids or formulationscontaining acids require solvents to stabilize the blend, especially incold climate conditions where freezing is an issue and pour points ofless than −40° C. are required. Inactive solvents comprise largeproportions of the total volume of a demulsifier blend, especially whenthe blend is used in cold climates. The purpose of such solvent isprimarily viscosity reduction to allow handling and prevent freezing.The problem is that such blends contain significant amounts of solvent.

For this reason it is desired to have a demulsifier blend that containsa comparatively smaller amount of solvent. It is also desired to have ademulsifier composition that is 100% active and comparativelyinexpensive.

SUMMARY

The present invention includes the use of anhydride compositions,including, for example, alkyl and aryl anhydrides, for use as ademulsifier in resolving water-in-oil emulsions. In particular, theanhydride composition can be used alone or in a blend with otherdemulsifiers. Specific anhydrides suitable for use in the presentinvention include acetic and propionic, with the preferred being aceticanhydride. The anhydride composition can be added directly to crude oilor other compositions to be resolved. As such, the demulsifiercomposition includes an anhydride alone or in combination with otherdemulsifiers. The anhydride especially acetic anhydride, can be used inan amount ranging between trace (which is around 0.5% or less by weight)and 100% by weight of the demulsifier composition.

This invention further relates to a demulsifier composition formed froma blend of demulsifier and the anhydride. The demulsifier includes ionicand non-ionic surfactants. Specific demulsifiers for use in thecomposition include alkylphenol resin, alkoxylates and derivatives,polyglycol ethers and derivatives, amine alkoxylates and derivatives,polyamine alkoxylates and derivatives, and combinations thereof. Thedemulsifier composition includes acetic anhydride in an amount rangingbetween about 1% and about 99% by weight of the composition. Morepreferably, the acetic anhydride is added in an amount ranging betweenabout 20% and about 80% by weight of the demulsifier composition. Evenmore preferably, the acetic anhydride is added in an amount rangingbetween about 30% and about 60% by weight of the demulsifiercomposition. As such, the anhydride can be used alone, so that theultimate demulsifier composition contains an amount of the anhydrideequal to between a trace amount and up to 100% by weight of thedemulsifier composition.

The invention also includes the use of anhydrides, especially aceticanhydride, as a solvent. Also, the invention includes using theanhydride blended alone or with a demulsifier to form a demulsifiercomposition in which the anhydride functions as a solvent. As such, anyamount of anhydride can be used as a solvent.

The invention further includes a method of forming a demulsifiercomposition. This includes adding at ambient conditions an amount ofanhydride to a known demulsifier.

Finally, the invention includes a method for dehydrating crude oil,whereby an amount of the demulsifier composition is added to the crudeoil. The demulsifier composition includes an anhydride, such as aceticanhydride, and potentially other constituents. The resultant demulsifiercomposition remains fluid at sub-zero temperatures including down to 40°C. below zero and lower.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and Examples.

DETAILED DESCRIPTION

The term “demulsifier” as used herein refers to a class of chemicalsused to aid the separation of emulsions (including water in oil, oil inwater, and multiple emulsions). They are commonly used in the processingof crude oil, which is typically produced along with significantquantities of saline water. This water (and salt) must be removed fromthe crude oil prior to refining, otherwise significant corrosionproblems can occur in the refining process. Demulsifiers are typicallybased on the following chemistry: acid catalysed phenol-formaldehyderesins, base catalysed phenol-formaldehyde resins, polyamines,di-epoxides, polyols. The above are usually ethoxylated (and/orpropoxylated) to provide the desired degree of water/oil solubility. Theaddition of ethylene oxide increases water solubility, whereas propyleneoxide decreases it. Commercially available demulsifier formulations aretypically a mixture of two to four different chemistries in a carriersolvent(s), such as xylene, heavy aromatic naptha, isopropyl alcohol,MeOH.

The term “acetic anhydride” as used herein refers to acetyl oxide oracetic oxide of the formula (CH₃CO)₂O. The acetic anhydride is acolorless, mobile, strongly refractive liquid. It is miscible withalcohol, ether, and acetic acid; and decomposes in water to form aceticacid.

The present invention relates to a demulsifier composition that includesanhydride and can include an amount of a known demulsifier. Suitableanhydrides include alkyl and aryl anhydrides, acetic anhydride beingpreferred. The resultant composition not only functions as ademulsifier, but is also a stable fluid at low temperatures.Specifically, the demulsifier composition functions in cold weatherenvironments of −40° C. and below and reduces the need for inactivesolvents. As such, the anhydride demulsifier composition of the presentinvention is effective for resolving a broad range of hydrocarbonemulsions encountered in crude oil production, refining, and chemicalprocessing. Typical hydrocarbons include crude oil, refined oil,bitumen, condensate, slop oil, distillates, fuels, brines, and mixturesthereof. The demulsifiers are also useful for resolving emulsions inbutadiene, styrene, acrylic acid, and other hydrocarbon monomer processstreams.

The anhydride offers demulsification performance similar to acids(organic or inorganic) but has an appreciable solubility forconventional demulsifier active ingredients. For example, aceticanhydride has a freezing point of −73° C., making it versatile not onlyas an active ingredient but also as a winterizing solvent. The aceticanhydride demulsifiers can be used to demulsify water-in-oil emulsionsin various production and refinery processes. In a refinery desaltingprocess, the incoming crude is deliberately mixed with wash water toremove dissolved salts and other contaminants. To extract water from theresulting water-in-crude oil emulsion, the emulsion is admixed with aneffective amount of the acetic anhydride demulsifiers. In the process ofresolving crude petroleum oil emulsions of the water-in-oil type, thedemulsifier compositions are brought into contact with or caused to actupon the emulsion to be treated in any of the various methods nowgenerally used in the petroleum industry to resolve or break crudepetroleum oil emulsions with a chemical agent.

According to an embodiment, the demulsifier composition comprises atleast an anhydride and can also be a blend of at least a “demulsifyingamount” of a demulsifier and anhydride, generally acetic anhydride.Demulsifiers, such as ionic or non-ionic surfactants, may be used aloneor in combination with any of a number of demulsifiers known in the artincluding fatty acids, fatty amines, glycols, and alkylphenolformaldehyde condensation products. Typical demulsifiers for breakingcrude oil emulsions that may have utility in the compositions herein aredescribed in U.S. Pat. Nos. 2,499,370; 2,557,081; 2,602,053; 3,640,894;3,699,894; 3,684,735; 4,537,701; and U.K. Patent No. 2,118,937A, all ofwhich are incorporated herein by reference.

Suitable “surfactants” are defined herein to include, but are notnecessarily limited to alkylphenol resin such as, oxyalkylated alkylphenol resins, oxyalkylated amines, glycol resin esters, polyglycolethers and derivatives, such as bisphenol glycol ethers, bisphenolglycol esters, salts of alkylaryl sulfonic acid, decarbamates,oxyalkylated polyols reacted with compounds selected from the groupconsisting of diepoxides and polycarboxylic acids, unreactedoxyalkylated polyols, unreacted oxyalkylated phenolic resins,alkoxylates and derivatives, amine alkoxylates and derivatives,polyamine alkoxylates and derivatives, and combinations thereof. Thederivatives include post-reacted materials such as polyglycol etherwhich is often reacted with another polyglycol ether using a linkingchemical. Conversely, the polyglycol ether may be reacted with a resin,or any of these compositions may be slightly reacted with, for example,a fatty acid.

In alternative embodiments, the particular demulsifier or solubilizingsurfactant used, as well as whether a single demulsfier or a combinationof demulsifiers is used, will depend upon the emulsion properties of theproduced fluids. The demulsifiers can be added in a variety of amountsincluding between broadly trace to about 100% or about 1% to about 99%by weight of the composition or between about 10% and about 90% byweight of the composition. More specifically, the demulsifier can beadded in an amount equal to between about 20% and about 80% by weight ofthe composition or, about 40% and about 70% by weight of the demulsifiercomposition. More preferably, the demulsifier is added in an amountequal to between about 25% and about 50% by weight of the demulsifiercomposition.

More specifically, the anhydride demulsifier composition (“demulsifiercomposition”) is formed from an amount of anhydride and optionally aknown demulsifier, such as the ones mentioned above. The anhydridesinclude alkyl and aryl anhydrides, specifically proprionic, maleic, andacetic anhydrides, with acetic anhydride being preferred. The anhydrideblended with the demulsifier is typically neat, or nearly 100% pure. Itcan be added in any amount sufficient to produce a demulsification andwinterizing solvent. The amount of anhydride mixed with the demulsifiercan vary according to a particular use; however, it is generally addedin an amount sufficient to prevent freezing of the demulsifier and allowfor use in cold climates.

The anhydride, and especially the acetic anhydride, can be added in anamount equal to between trace and up to 100% by weight of thedemulsifier composition. If the acetic anhydride is to be used as aprinciple solvent then it will preferably be added in an amount equal tobetween about 20% and about 80% by total weight of the demulsifiercomposition. More preferably the acetic anhydride is added in an amountequal to between about 30% and about 60% by weight of the demulsifiercomposition. The acetic anhydride can also be added in an amount equalto between about 50% and about 75% by weight of the demulsifier. In analternative, other solvents may be included with the anhydride wherebyit can be added in an amount ranging between about 1% and about 10% bytotal weight of the demulsifier composition. Again, broadly, thedemulsifier composition can include an amount of anhydride, includingacetic anhydride, ranging between trace or about 1% and up to about 99%or 100% by weight of the demulsifier composition.

The demulsifier composition may also include corrosion inhibitors,viscosity reducers and other chemical treatments used in crude oilproduction, refining and chemical processing. Additional optionalsolvents could be added such as: xylene, toluene, light or heavyaromatic naphtha, and the like. Each component contributes to differenttreating characteristics when added to the crude oil emulsion due totheir unique chemical properties.

In a typical application, the acetic anhydride alone or with ademulsifier is blended together to form a chemical treatment suitablefor application to the emulsion. The amount of the demulsifiercomposition used depends on the particular crude oil emulsion beingtreated. Although the amount added is typically at least 10 ppm. Ingeneral, the effective amount of demulsifier composition ranges frombetween about 10 ppm to about 1,000 ppm based on the volume of oil. Forexample, the demulsifier composition can be introduced into the crudeoil emulsion by injecting beneath the surface into the oil well itselfby injecting into the crude oil at the well-head or by injecting intothe crude oil process stream at a point between and including thewell-head and the final oil storage tank. The demulsifier compositionmay be injected continuously or in batch fashion. The injection step ispreferably accomplished using electric or gas pumps.

The treated crude oil emulsion is then allowed to separate into distinctlayers of water and oil. Once separation into distinct layers of waterand oil has been effected, various means known in the art can beutilized for withdrawing the free water and separating crude oil.

In a typical process for demulsification of crude oil, a reservoir isprovided to hold the composition of the invention in either diluted orundiluted form adjacent to the point where the effluent crude petroleumoil leaves the well. For convenience, the reservoir is connected to aproportioning pump capable of dropwise injecting the demulsifier of theinvention into the fluids leaving the well, which then pass through aflow line into a settling tank. Generally, the well fluids pass into thesettling tank at the bottom of the tank so that incoming fluids do notdisturb stratification of the layers of crude petroleum oil and waterthat takes place during the course of demulsification.

The foregoing may be better understood by reference to the followingexamples, which are intended for illustrative purposes and are notintended to limit the scope of the invention.

EXAMPLE 1

Listed below are a variety of compositions that were tested asdemulsifiers. The testing was performed as a typical bottle test where100 ml of warmed oil emulsion was contacted for a period of time with ademulsifier. The oil contained water in an amount equal to 15% by volumeof the total mixture. The emulsions were heated to about 80° C. Thedemulsifiers were added as listed below in an amount ranging betweenabout 300 ppm to about 2400 ppm. The emulsion and demulsifier mix wasshaken.

Water drop/ml (monitored over time) Residual water in Chemical Dose/ppm15′ 25′ 1 h 2 h oil/% D-88 + D-87 300 + 300 0 0 1 3 11.5 600 + 600 0 1 814 2.4 900 + 900 0 1 10 14 2.1 1200 + 1200 2 4 13 15 1.3 215.1 300 2 413 15 1.2 600 5 9 12 15 1.2 900 6 10 13 15 1.1 1200  8 11 13 13 0.8

Performance of the chemical treatment was evaluated by means ofmonitoring the volume of water that phase separated in the bottle overtime (15 minutes, 25 minutes, 1 hour, and 2 hours) and also bydetermining the amount of residual water (percentage by volume) thatremained in the oil at the end of the 2 hour period (far right column).

The two formulations D-87 and D-88 were designed to treat an oilfieldemulsion in Northern Alberta. The demulsifier and acid blends were bothrequired to dehydrate the crude oil. Neither is capable of treatment onits own and treatment rates of both are high. D-88 is a conventionaldemulsifier blend comprising about 40% active ingredients (polymericalkoxylates and derivatives) and about 60% inactive solvent (alcohol andaromatic hydrocarbon). D-87 is a 50% active solution of acetic acid inxylene and isopropyl alcohol. These solvents are required to prevent theacetic acid from freezing (it has a melting point of 16° C.).

Blend 215.1 is a novel blend comprising demulsifier active ingredientsfrom D-88 (25%) and acetic anhydride (75%). The laboratory test datashows that at 300 ppm this single blend performs equivalently to 1200ppm D-88 plus 1200 ppm D-87.

EXAMPLE 2

Acetic anhydride is used as a demulsifier. Tests are performed whereby atypical bottle test of 100 ml of warmed oil emulsion is contacted for aperiod of time with the acetic anhydride demulsifier. The oil containswater in an amount equal to 15% by volume of the total mixture. Theemulsions are heated to 80° C. The acetic anhydride is then added in anamount ranging between 300 ppm and 2400 ppm. The emulsion anddemulsifier mix is shaken.

Performance of the chemical treatment is evaluated by means ofmonitoring the volume of water that phase separates in the bottle overtime (15 minutes, 25 minutes, 1 hour, and 2 hours) and also bydetermining the amount of residual water (percentage by volume) thatremains in the oil at the end of the 2 hour period. The results willshow that water is separated, and the residual water is less than 1.2%.

While the invention has been explained in relation to exemplaryembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thedescription. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

The claimed invention is:
 1. A method of demulsifying an oil and wateremulsion, wherein the oil is a crude oil, the method comprising: a)forming a demulsifier composition including an anhydride in an amountranging between about 25% and about 50% by weight of the demulsifiercomposition, wherein the demulsifier composition remains fluid attemperatures down to about 40° C. below zero and lower, and wherein thedemulsifier composition further comprises a component selected from thegroup consisting of: alkylphenol resins; alkoxylates and derivatives;polyglycol ethers and derivatives; amine alkoxylates and derivatives;polyamine alkoxylates and derivatives; oxyalkylated amines; glycol resinesters; salts of alkylaryl sulfonic acid; dicarbamates; oxyalkylatedpolyols reacted with diepoxides and polycarboxylic acids; unreactedoxyalkylated polyols; unreacted oxyalkylated phenolic resins;alkoxylates and derivatives; and combinations thereof; b) injecting thedemulsifier composition beneath a surface into an oil well; and c)separating the oil from the water.
 2. The method of claim 1, wherein thedemulsifier composition further comprises additional solvents.
 3. Themethod of claim 1, whereby the anhydride is selected from the groupconsisting of: alkyl anhydrides and aryl anhydrides.
 4. The method ofclaim 1, whereby the anhydride is selected from the group consisting of:propionic anhydride, maleic anhydride, and acetic anhydride.